1. Field of the Invention
The present invention relates to a printer and more particularly to the printer having a plurality of contact electrodes and a plurality of contact electrodes that correspond to the contact electrodes, wherein the contact electrodes and corresponding counter electrodes are brought into electrical connection by being pressed together.
2. Description of the Related Art
Japanese Patent Application Kokai No. HEI-3-101944, for example, describes a type of contact electrode connector used in an ink jet printer. The contact electrode connector is for connecting a print head to a flexible circuit.
The print head of an ink jet printer includes a plurality of ink droplet generators. The ink droplet generators are provided aligned in a surface of the print head. Each ink droplet generator includes a nozzle, an ink chamber, a thermal resistor, and an ink supply channel. The nozzles of the ink droplet generators appear aligned along the surface of the print head. Each nozzle is provided to its corresponding ink chamber so as to bring the ink chamber into fluid connection with the atmosphere. Each ink supply channel is formed in a wall of its corresponding chamber. Each thermal resister is formed in another wall of its corresponding chamber.
When a voltage is applied to a thermal resistor, the energized thermal resistor generates heat. The head vaporizes ink that fills the ink chamber and that is in contact with the thermal resistor. The vaporized produces an expanding bubble that forces ink from the nozzle by the force of its expansion. By selectively energizing thermal resistors provided to the plurality of ink droplet generators in the print head, ink droplets can be produced on demand. To print an image on a recording sheet scanningly transported in front of the print head, the thermal resistors are selectively energized according to print information from, for example, a central processing unit (CPU) in the printer.
Typically, the print head is integrally provided with an ink tank to form an ink cartridge. The ink tank is for storing ink to be supplied to ink droplet generators via the ink channels. The ink cartridge is provided to a carriage capable of reciprocally scanning across the widthwise surface of the sheet to be recorded on. The ink cartridge is provided detachably to the carriage to enable replacement of the ink cartridge when ink stored in the ink tank is used up. A flexible circuit formed on a flexible resin substrate is provided for transmitting print information from the CPU to the print head. A plurality of contact electrodes are provided to the surface of the flexible circuit. A plurality of counter electrodes are provided to the surface of the print head at positions corresponding to positions of the contact electrodes. The contact electrodes and the counter electrodes are for electrically connecting the print head of a replacement ink cartridge with the flexible circuit.
Japanese Patent Application Kokai No. SHO-62-234942 describes a contact electrode connector for providing electrical connection between thermal resistors in a print head and a CPU in a printer. As shown in FIG. 1, the contact electrode connector includes a print head portion 63, a flexible circuit portion 53, and a carriage portion 76.
The print head portion 63 includes a rigid head substrate 60 and counter electrodes 62 formed thereto. The counter electrodes 62 are for transmitting pulses of voltage to the thermal resistors (not shown) in the print head.
The flexible circuit portion 53 includes a flexible substrate 50, protruding portions 51 formed in the flexible substrate 50, and contact electrodes 52, one contact electrode being formed to each protruding portion 51. The protruding portions 51 are formed at positions in the flexible substrate 50 corresponding to positions of the counter electrodes 62 in the head substrate 60. The protruding portions 51 support corresponding contact electrodes 52 above the surrounding level surface of the flexible circuit portion 53. Each protruding portion 52 has a concave underside opposite the surface on which the corresponding electrode is formed.
The back up member 76 includes a support plate 70 and rubber protrusions 77 formed to the surface of the support plate 70. The support plate 70 is provided to a carriage (not shown) of the printer. The rubber protrusions are provided at positions corresponding to positions of the protruding portions 51 so as to abut the concave underside of corresponding protruding portions 51.
As shown in FIG. 1, when the contact electrode connector is assembled into the connected condition, the flexible circuit portion 53 is sandwiched between the head substrate 60 and the support plate 70 so that the contact electrodes 52 are brought into contact with corresponding counter electrodes 62. The rubber protrusions 77 abut the back surface of the protruding portions 51, thereby pressing the contact electrodes 52 against their corresponding counter electrodes 62.
However, there has been know a problem with replaceable ink cartridges in that a user can damage the contact terminal connector by applying excessive force when replacing the ink cartridge. For example, the protruding portions 51 can be plastically crushed if the counter electrodes 62 and the contact electrodes 52 are pressed together with excessive force. This is especially a problem when the protruding portions 51 are not properly aligned with corresponding rubber protrusions 77.
Electrical contact between a contact electrode 52 and its corresponding counter electrode 62 is usually formed at the tip point of the contact electrode 52. The tip point of a contact electrode corresponds to the tip of the protruding portion 51 that protrudes furthest from the surrounding level surface. However, when the contact electrodes 52 can move relative to and therefore abrade against corresponding counter electrodes 62, for example, during movement of the carriage or replacement of the ink cartridge. Because contact electrodes 52 contact corresponding counter electrode 62 at only a single tip point, they are less durable and so can be worn down more quickly.
When, as described above, the protruding portions 51 of the flexible circuit 53 are crushed, or the contact electrodes 52 damaged or abraded, electric contact between the contact electrodes 52 and corresponding electrodes 62 can become defective. Defective electric contact prohibits application of voltage to the thermal resistors in the head so that corresponding drop generators can not be caused to eject ink droplets on demand. Therefore, the flexible circuit 53 must be replaced when the contact electrodes 52 are damaged or abraded. However, because the flexible circuit 53 is fixed to the printer, the user must hire a professional no replace the flexible circuit 53. This repair can be expensive. This becomes a problem not only with ink cartridges wherein the head and the ink tank are integratedly formed, but with all replaceable heads.
Another problem leading to possible poor contact between the contact electrodes 52 and corresponding counter electrodes 62 is caused by excess variation in the amount at which protruding portions 51 are raised above the surrounding level surface of the flexible substrate 50. Although slight variation in the height of protruding portions 51 can be absorbed by deformation of the protruding portions 51, stress to the support plate 70 increases radically in a non-linear fashion relative to the amount of deformation. Because of this, when the variation in height of the contact electrodes exceeds a certain amount, some contact electrodes will bear an extremely large stress while others will bear almost none. The contact electrodes bearing very little stress often are sources of poor or defective contact.
Poor or defective contact between corresponding contact electrodes and counter electrodes can also occur when the resin substrate of the flexible circuit plastically deforms during production of the protruding portions.